1. Field of the Invention
The skin is an organ in its own right, playing a fundamental role in health and also in the appearance. A barrier which is both resistant and fragile, it undergoes perpetual renewal. Despite this, the first signs of skin ageing manifest themselves discreetly before 30 years of age. With time, the skin loses its suppleness and its ability to retain water decreases. Although dehydration is only one of the aspects of skin ageing, it appears that the water content is closely linked to a number of morphological and molecular characteristics of normal skin.
2. Description of Related Art
The protection against water loss is mainly provided by the epidermis and its horny layer (Verdier-Sevrain., S. & F., Bonte, 2007, J. Cosmet. Dermatol. 6(2): pp 75-82). The epidermis is a stratified squamous epithelium consisting mainly of keratinocytes (90%), the dermis being the connective feeder support for the epidermis, the main biological purpose of which is the formation of the horny layer. The “stratum corneum” or horny layer is the most superficial zone of the epidermis. It consists of a stack of flat anuclear cells, corneocytes, which are the end result of the keratinocyte differentiation and proliferation process. By virtue of its solidity and its compact stratified structure, the stratum corneum ensures a barrier function: it opposes transcutaneous water loss and protects the underlying layers against mechanical and chemical attacks and ultraviolet irradiation.
The water content of the skin is conditioned by various parameters, among which are, inter alia, the degree of water elimination, which depends on the balance which exists between the ability of the skin to retain water and the transepidermal losses due to evaporation, a type of physiological dehydration reflecting the integrity of the epithelial skin barrier and also its functionality.
All epithelia, including that of the skin, comprise cells that are associated with one another with more or less cohesion. Tight junctions are specific to all epithelial tissues. Generally located at the top of the cells, they seal skin epithelial cells to one another and thus prevent the intercellular passage of fluids out of tissues. Their principal function is therefore to ensure the leaktightness of the epidermis and to prevent the organism from losing all its water on contact with the outside environment (Tsuruta, D., et al., 2002, Trends Cell Biol. 12(8): pp 355-7).
The junction between epidermal cells is in fact due to homophilic interactions which involve several adhesion proteins. The first is occludin (from the Latin word occludere=to trap). It is a transmembrane protein having a weight of 64 kDa, comprising a polypeptide chain which crosses the membrane four times. The second is claudin (from the Latin word claudere=to close), a transmembrane protein having a weight of 22 kDa, also comprising a polypeptide chain which crosses the membrane four times. Claudin is part of a family of at least 24 members, several of which may be present in the same junction. The third protein is JAM (junctional adhesion molecule), a protein having a molecular weight of 33 kDa, and the polypeptide chain of which crosses the membrane just once.
Occludin, claudins and JAM assembled form a network of fibrilles which encircle the apical domain of epithelial cells. The tight junctions are bound to intracellular proteins such as ZO-1 and ZO-2 (zonula occludens) which, in turn, are bound to the cytoskeleton (actin). This interaction with the cytoskeleton determines the location of the junction at the apical domain of the cell.
Depending on the expression of the proteins which constitute the tight junctions, the epidermal cells are more or less capable of limiting the permeability of the skin epithelium. The hydration of the skin remains a complex phenomenon which is of essential importance in cosmetology or in dermatology, hence the constant search for new treatments which reprogram the process of deep and surface hydration for replumping the skin from the inside and smoothing out the contours of the skin.
Lentinus edodes (shii-take), an edible forest mushroom from Japan, is known in many Asian countries (China, Korea, etc.) to be one of the best mushrooms for its taste and its fragrance. Lentinus edodes is in fact characterized by a number of specific substances, for instance guanosine 5′-monophosphate which induces a pleasant fragrance and an aromatic substance, lenthionine.
Hundreds of edible mushrooms currently exist around the world, but the majority are not cultivated. Only a few mushrooms, Agaricus bisporus in Europe and Lentinus edodes in Asia, are cultivated on a large scale, but Agaricus bisporus is cultivated on compost and used fresh, whereas Lentinus is cultivated on wood and often dried. This is because the drying of Lentinus makes it possible to conserve it, while at the same time preserving its aroma and its taste.
The shii-take is an expensive mushroom which is also known as “elixir of life”. According to the great Chinese physician WU SHUI, who lived at the time of the Ming dynasty (1364-1644), the shii-take increases vigour and vitality and is very effective in the preventive treatment of brain haemorrhage. Recently, the medical properties of the shii-take have been studied by Japanese researchers and it has been possible to demonstrate antiviral, antibiotic, antitumour and blood-lipid-lowering actions.
Approximately 800 years ago, the mushroom began to be cultivated in China (the Chinese name for shii-take is HOANG-KO). Today, close to 230 000 small producers of shii-take exist in Japan. This mushroom is also cultivated in Korea and in China and is collected in the wild state in forests in other Asian countries. In 1974, the total production in Japan was 12 000 tonnes of dried mushrooms and 55 000 tonnes of fresh mushrooms. The shii-take is only exported dried.
An aqueous extract of Lentinus rich in lentinan is known, from patent FR2776184, for its antitumour properties. Patent FR2829389 describes a method for extracting Lentinus, comprising steps of enzymatic hydrolysis in order to obtain an extract capable of inhibiting the activity of certain metalloproteases, MMPs, and in particular MMP-1 and MMP-2.
The chemical composition of the shii-take has been determined by standard analytical methods published by the Analytical Chemistry Association. The quantitative determinations related to water content, crude proteins, fats and ash. The crude proteins were determined relative to the nitrogen contained, assayed by the Kjeldahl method, using the conversion factor (N×6.25). In fact, the studies and assays carried out on the crude protein show that only a part is digestible. Other studies demonstrate that the probable degree of digestibility is 60-70%. This reduced degree is explained by the fact that the mushrooms contain a not insignificant percentage of non-protein nitrogen bound to the chitin of the cell walls. It can therefore be considered that the conversion factor is 70% N×6.25 or (N×4.38).
The percentage of fat contained in the mushrooms can range between 1% and 15%-20% of the dry weight. On average, the mushrooms contain 2% to 8% of fats and all the lipid categories are found therein, such as free fatty acids (stearic acid, oleic acid, palmitic acid and linoleic acid), mono-, di- and triglycerides, sterols (ergosterol), sterol esters and phospholipids. The fats have been analysed by extraction with solvents; the fibre, as residue after digestion; the ash as residue after incineration. The fresh mushrooms contain between 3% and 28% of carbohydrates and 3% to 32% of fibre. The carbohydrates have been calculated by difference, as total carbohydrates (fibre included) or as carbohydrates without fibre. It may be considered that the greatest amount of non-protein nitrogen is in the form of chitin and a small amount is in the form of urea or of ammonium salts.
CrudeCarbohydratesEnergyWaterproteinWithoutvalueSamplecontentN × 4.68FatTotalNFibreAshKcalDried (1)15.810.31.92.35.86.55.5375Dried (4)19.526.02.95.01.513.56.1345Dried (3, 4)18.413.11.29.24.514.76.5333Fresh (3, 4)90.017.58.07.59.58.07.0387Fresh (2)91.813.44.98.00.77.33.7392(1) - Singer (1961)(2) - Agrofoods Organization (1972)(3) - Soweda (1965)(4) - Adriano and Gruz (1933)
Lentinus edodes contains 17.5% of its dry weight in proteins and virtually all the essential amino acids. Approximately 25-35% of the total amino acids are free amino acids, the remainder being protein-bound. In addition to the common amino acids, rare amino acids or nitrogenous substances such as: β-alanine, methionine sulphoxide, cysteic acid, hydroxyproline, hydroxylysine, α-aminoadipic acid, α, β and γ-aminobutyric acid, pipecolic acid and 5-hydroxypipecolic acid, phosphoserine, cystathione, canavanine, creatinine, citrulline, amithine, glucosamine and ethanolamine have been detected in these mushrooms.
Amino acid composition of Lentinus edodes according to Kagawa (1970), Sawada (1965), Sugimosi et al. (1971)
mg of amino acids per gram ofAmino acidcrude protein.Isoleucine218Leucine348Lysine174Methionine87Phenylalanine261Cystinenot determinedTyrosine174Threonine261Tryptophannot determinedValine261Arginine348Histidine87Alanine305Aspartic acid392Glutamic acid1182Glycine218Serine261Total amino acids4962
Pentoses (xylose and ribose), methyl pentoses (rhamnose and fucose), hexoses (glucose, galactose and mannose), disaccharides (sucrose), amino sugars (glucosamine and N-acetylglucosamine), sugar alcohols (manutol and inositol), sugar acids (galacturonic and glucuronic acid), etc., are found in mushrooms of the Lentinus genus. Mannitol is present at a high concentration (9-13%).
The Lentinus mushroom contains polysaccharides and chitin (polymer of N-acetylglucosamine). Similarly, α,α′-trehalose, commonly known as mushroom sugar, is found.
The vitamins that are most widespread in the shii-take mushroom are thiamine, riboflavin, niacin and biotin. Vitamin A (retinol) is not usually found in these mushrooms, but provitamin A, expressed in β-carotene equivalents, can sometimes be assayed. Similarly, vitamin D is rare, but ergosterol, which can be converted to vitamin D by ultraviolet irradiation, is found.